The present invention relates, in general, to an ultrasonic surgical device for cutting and coagulating tissue that utilizes closed-loop feedback and, more particularly, to a control method and apparatus for controlling the heat treatment of tissue in separate modes for ultrasonic cutting and ultrasonic coagulation.
Ultrasonic instruments, including both hollow core and solid core instruments, are used for the safe and effective treatment of many medical conditions. Ultrasonic instruments, and particularly solid core ultrasonic instruments, are advantageous because they may be used to cut and/or coagulate organic tissue using energy in the form of mechanical vibrations transmitted to a surgical end-effector at ultrasonic frequencies. Ultrasonic vibrations, when transmitted to organic tissue at suitable energy levels and using a suitable end-effector, may be used to cut, dissect, or cauterize tissue. Ultrasonic instruments utilizing solid core technology are particularly advantageous because of the amount of ultrasonic energy that may be transmitted from the ultrasonic transducer through the waveguide to the surgical end-effector. Such instruments are particularly suited for use in minimally invasive procedures, such as endoscopic or laparoscopic procedures, wherein the end-effector is passed through a trocar to reach the surgical site.
Ultrasonic vibration is induced in the surgical end-effector by, for example, electrically exciting a transducer which may be constructed of one or more piezoelectric or magnetostrictive elements in the instrument hand-piece. Vibrations generated by the transducer section are transmitted to the surgical end-effector via an ultrasonic waveguide extending from the transducer section to the surgical end-effector.
U.S. Pat. No. 5,322,055 describes an ultrasonic surgical apparatus that includes a surgical instrument having a transducer for converting an electrical signal into longitudinal vibratory motion. The longitudinal vibratory motion is transmitted to an ultrasonic blade that is connected to the hand-piece. An accessory is releasably connected to the hand-piece to enable clamping of tissue against the vibrating blade to afford improved coagulating and cutting of tissue. In U.S. Pat No. 5,322,055 scissors-like grips actuate a pivoted clamp jaw along one side of the ultrasonically vibrating blade to compress and bias tissue against the blade in a direction which is substantially normal to the direction of longitudinal vibratory motion.
Hemostatic devices have been described in various instruments for cutting, cauterization, coagulation or tissue welding. Most of the devices used are either monopolar or bipolar, for example, bipolar forceps, monopolar or bipolar scissors, and cutting and coagulating devices. See, for example, U.S. Pat No. 5,707,369 that describes a temperature feedback system for closed loop control of the tissue temperature induced by the surgical instrument wherein a function of the temperature is used to determine when coagulation of tissue has occurred to a desired degree.
Although open loop energy instruments have been used successfully to control bleeding during surgical procedures, when such instruments are used, the primary control is the experience of the surgeon who responds to what is observed to be happening to the tissue as it is treated with energy. Often, particularly for endoscopic procedures, surgeons cannot readily see what is happening to the tissue. In addition, tissue properties may change quickly during energy delivery. A surgeon""s reaction time may be insufficient for optimal efficacy. Consequently, the tissue treatment may not be as precisely controlled as may be desirable. Some problems that may occur include tissue charring, sticking of the tissue to the electrodes of the surgical instrument, and over or under treatment of the tissue.
Temperature-measuring devices have been described for use with tissue treating instruments to measure temperature and determine when the absolute temperature has exceeded a desirable temperature. These devices are typically used to signal to a user to turn off energy or to cause a control device to turn off or attenuate energy when the temperature has reached a level at which tissue sticking to the instrument may occur. Other instruments have used temperature feedback to maintain a set temperature to follow a predetermined temperature profile.
Notwithstanding these control arrangements, there is a continuing need for improvement in the control of heat energy delivery to the tissue and/or determination of when tissue treatment has reached an optimal level. In particular there is a need to provide a device and method for ultrasonic instruments that must perform both cutting and coagulating functions, and to provide closed loop feedback for separate cutting and coagulating aspects. This invention fulfills these needs.
The present invention is an ultrasonic surgical instrument incorporating a closed-loop feedback system that controls the energy delivered by the instrument into tissue. Accordingly, one embodiment of the present invention provides a temperature monitoring device and/or method which controls the tissue temperature at the end-effector of a therapeutic ultrasonic cutting and coagulating instrument as the tissue is being heated with ultrasonic vibrations from the instrument""s end-effector. Based on a model of the behavior of tissue temperature (which may be inferred from instrument temperature) with the delivery of therapeutic energy, the monitored tissue (or instrument) temperature is used to control the coagulation phase, or the cutting phase, of tissue.
A temperature sensor is located at the end-effector, preferably on a clamping member. The temperature sensor measures the temperature of the tissue engaged by the end-effector either directly or indirectly. In the instrument, the temperature-measuring device may be in contact with the tissue or may indirectly measure temperature of the tissue by measuring the temperature of the end-effector. The temperature-measuring device preferably comprises a temperature transducer that changes the temperature measurement into a corresponding electrical signal indicative of the temperature at the temperature transducer. The signal from the temperature transducer is provided to feedback control circuitry and a device for selecting a function of the instrument for either cutting mode or coagulating mode.
When the temperature reaches the desired level for the selected function, indicating a desired tissue condition, a signal is provided to a control unit or the user, at which time the energy supply is switched off or attenuated. The feedback signal may, for example, provide a visual audible or tactile signal to a user, and/or may provide instructions to a control unit to automatically alter the energy supply to the tissue.
The energy source may be responsive to a power control signal of a controller. The feedback circuitry may be coupled to, or included with, the power controller. The power controller may include at least one electrical switch for selectively controlling the energy supplied to the instrument to coagulate tissue, or to cut tissue, depending on the electrical switch setting.
In accordance with another aspect of the present invention, a method of operating an apparatus for surgically heat treating tissue during surgical procedures is provided. Accordingly a preferred method comprises the steps of: selecting an operational mode of an ultrasonic surgical instrument, engaging tissue to be surgically treated with the end-effector of the ultrasonic surgical instrument; applying therapeutic tissue heating energy to the tissue to be treated; measuring the temperature of the tissue as it is being treated; generating a signal representative of the temperature of the tissue; and controlling the therapeutic tissue heating energy applied to the instrument in response to the temperature signal.
Another method of performing the present invention includes the steps of: supplying ultrasonic energy to tissue in the form of mechanical vibrations of an ultrasonic end-effector, supplying high-frequency electrical energy to tissue, measuring tissue electrical impedance, and altering the output of the ultrasonic generator in response to a measured tissue electrical impedance parameter.